This invention describes a semiconductor imaging device for radiation imaging. The imaging device is an array of image cells, which consists of an array of radiation detector cells and an array of image cell circuits. An example of an imaging system configuration is shown in FIG. 1 of the accompanying drawings. All cells in the detector cell array are connected to respective electronics cells in the array of image cell circuits. With appropriate processing technology, it is possible to implement both detector cells and circuit cells on the same substrate. Another possibility is to have two substrates, one for the detector and one for the cell circuits and, by using a bump-bonding or other technique connect them mechanically and electrically together so that each detector cell is connected to the corresponding cell circuit. A cross-section of a part of an imaging device made of two substrates, which are bump-bonded together, is shown in FIG. 2 of the accompanying drawings.
In many radiation imaging applications, a need for different image resolutions exist. In single exposure images, the resolution should usually be relatively high. On the other land, the same imaging system could be used for displaying live image by continuously reading the image from the imaging device and updating the display in real time. However, if the imaging system is designed for high resolution, the data bandwidth for a live image at, for example, 30 frames per second may be so high that the requirements for the readout electronics for handling the data stream may become unreasonable. A readout system fast enough to capture and process the images could become unreasonably expensive compared to the total cost of the imaging system. Furthermore, a high image resolution required for single exposure images may not even be required for a live display of images.
Therefore, a method for effectively reducing the resolution and thus the data bandwidth on chip would solve the problem. Another problem is the scalability of the imaging system for large or small area imaging systems. If single imaging devices with relatively small area could be easily linked together to form a seamlessly connected array of imaging devices for large area imaging system, the same imaging devices could easily be used for either large and small area applications.
A further problem encountered with imaging devices is that distributed capacitance associated with the on-chip read-out lines can result in current spikes during read-out resulting in longer settling times for the read-out circuitry and consequently reducing the speed at which data can be read from the imaging device.
This invention tries to solve at least one of the problems referred to above.
Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from dependent claims may be combined with those of the independent claims in any appropriate manner and not merely in the specific combinations enumerated in the claims.